During operation of an automotive vehicle's internal combustion engine, some fraction of the fuel introduced into the engine combustion chambers is not fully combusted and remains as an undesirable constituent of the exhaust. In order to promote complete combustion of such residual constituents, secondary air may be pumped into the exhaust before the exhaust is discharged to atmosphere, and typically this is done by means of an air pump. In addition to the air pump, a known type of secondary air system further comprises an electric ported vacuum valve, an air (flow) control valve, and a check valve.
This known system operates by an electric signal input to the ported vacuum valve causing the ported vacuum valve to deliver vacuum to the air valve. The air valve opens to allow air to be pumped from the air pump into the exhaust.
Occasionally back pressure from the exhaust can exceed the air pressure from the pump, and therefore to protect the pump from the backflow of potentially damaging hot exhaust gasses, a one-way (unidirectional) check valve is disposed between the air pump and the exhaust to block any potentially damaging backflow to the air pump.
Some embodiments of this known type of system possess certain potential disadvantages. One potential disadvantage is that three separate assemblies may be required in addition to the air pump; another is that a wiring harness is required to connect to the automotive vehicle's electrical system; still another is that the operating threshold of the check valve can be inconsistent, thereby potentially limiting use to only "high" pressure situations; and yet another is that it does not use operating parameters (air and exhaust pressures) to optimize performance.
The present invention provides improvements that can overcome such disadvantages. The invention can embody all required protection and control functions in a single air flow/check valve assembly. The assembly can be entirely mechanical so that there is no need for electrical wiring harness connection of the assembly into the electrical system. In a general way, the invention may be briefly described as comprising an assembly for sensing the pressure differential across a valve seat and causing the sensed pressure differential to control a vacuum signal for opening and closing a valve member from and against the valve seat to thereby perform air flow/check valve functions. The assembly is also capable of providing protection of the air pump against a series of exhaust pressure surges which collectively, but not individually, may be capable of creating potentially damaging backflow from the exhaust to the air pump.
Further features, advantages, and benefits of the invention will suggest themselves to the reader as the disclosure of the invention proceeds. Drawings accompany the written description, and portray a presently preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.